1. Field of the Invention
The present invention generally relates to a method of processing a substrate with cyclic plasma by, e.g., plasma-enhanced atomic layer deposition (PEALD) or other low-power cyclic plasma-assisted processes, particularly to a method for controlling such processes based on plasma ignition status.
2. Description of the Related Art
In deposition of film in a PEALD reactor using low RF power, failure of plasma ignition may occur despite RF power being ON. Depending on the frequency of failure of plasma ignition, it will be difficult to obtain a film having targeted quality, resulting in generation of defective wafers. Thus, it is important to monitor the status of plasma discharge.
However, it is difficult to accurately monitor the status of plasma discharge for film deposition by PEALD or the like when plasma is charged intermittently or in pulses. Unless a proper monitoring system and parameters are established, anomalous pulses of RF power cannot accurately be detected.
For example, FIG. 1 is a schematic diagram illustrating an RF power monitoring system for a cyclic plasma-assisted reactor such as a PEALD reactor. It should be noted that any discussion of problems and solutions involved in the related art and the schematic diagram of FIG. 1 have been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion and the schematic diagram of FIG. 1 were known at the time the invention was made.
In FIG. 1, a main control unit (not shown), which is a controller above all, communicates with a dual chamber module controller (“DCMC”) 1 using transmission control protocol and internet protocol, for example, which module controller controls process modules including a process module for controlling an RF generator. DCMC 1 communicates with an analog digital system (“ADS”) 4 via a DeviceNet (a network system used in the automation industry to interconnect control devices for data exchange), for example. ADS 4, which is disposed between DCMC 1 and an I/O interface board of a reactor 3 such as a PEALD reactor or cyclic PECVD reactor, receives control commands from DCMC 1, converts digital signals of the commands to analog signals and outputs a bit sequence to respective digital out ports. ADS 4 also converts analog and digital signals from the reactor 3 and outputs them to DCMC 1. DCMC 1 outputs all analog output and digital output settings to ADS 4, and ADS 4 outputs all analog input and digital input current values to DCMC 1.
The system illustrated in FIG. 1 further comprises a programmable logic controller (PLC) logger 2 for monitoring, which receives RF signals such as RF power output, RF power ON status, RF forward power, RF reflected power, RF peak-to-peak voltage (Vpp), and RF DC bias (Vdc) from the reactor 3, and outputs, to DCMC 1, RF status indicative of whether the measured time period of RF power ON status is longer than the time period of RF power output, whether the value of RF forward power exceeds a set threshold after a set delay time elapses since the start of RF power ON, whether the value of RF reflected power exceeds a set threshold after a set delay time elapses since the start of RF power ON, whether the value of Vdc exceeds a set threshold since the start of RF power ON, and whether a difference between the timing of RF power OFF and the timing of RF forward power OFF exceeds a set value. If DCMC 1 sets an alarm which is raised according to the RF status reported from PLC logger 2, DCMC 1 raises an alarm. PLC logger 2 begins logging when DCMC 1 outputs a PLC command to start, and ends logging when DCMC 1 outputs a PLC command to end.
However, according to the system described above, it cannot accurately detect anomalous pulses of RF power such as plasma ignition failure pulses (pulses indicative of failure of plasma ignition) or cannot quantify anomalous pulses of RF power, and thus, no proper countermeasure for anomalous pulses of RF power can be set.